Get used to it

Meaning

Accept that a particular state of affairs is inevitable.

Origin

This began to be used as a single sentence, with the meaning - 'that's how things are; accept it', from around the early 1990s in the USA. Here's an early example, from a report of a Gay Pride march in Washington, USA, in April 1993, by Simon Tisdall in The Guardian:

"'We're queer, we're here. Get used to it,' said T-shirts worn by some of the marchers..."

Note: the 'we're here, we're queer' slogan began just a few years earlier. The earliest reference I can find for that is from 1990.